It’s Biden:

Sen. Barack Obama has selected Delaware Sen. Joe Biden as his running mate, according to his official Web site and a text message the campaign sent to supporters on Saturday.

“Barack has chosen Senator Joe Biden to be our VP nominee,” the text message, sent at around 3 a.m. ET, said.

“Joe and I will appear for the first time as running mates this afternoon in Springfield, Illinois — the same place this campaign began more than 19 months ago,” Obama said in an e-mail sent to supporters Saturday morning.

“I’m excited about hitting the campaign trail with Joe, but the two of us can’t do this alone,” he wrote. ” We need your help to keep building this movement for change.”

Vice presidential candidates are often called on to be the aggressors in the campaign. A comment Biden made earlier this year may have resonated with Obama:

“I refuse to sit back like we did in 2000 and 2004. This administration is the worst administration in American foreign policy in modern history — maybe ever. The idea that they are competent to continue to conduct our foreign policy, to make us more secure and make Israel secure, is preposterous. … Every single thing they’ve touched has been a near-disaster.”

Updated by JP at 5:27 a.m.